1. Field of the Invention
This invention relates to the making of keys for tumbler and wafer type locks, and more particularly concerns a system for determining how to make a key to replace a lost key for a specific tumbler or wafer lock.
2. Description of the Prior Art
In cylinder locks of conventional design, a cylindrical plug having a key receiving slot or xe2x80x9ckeywayxe2x80x9d bounded by straight upper and lower border surfaces, and having a first series of radially disposed channels communicating with said upper border surface is rotatably secured within a close fitting cylindrical bore in a housing having a second, matching series of channels, known as xe2x80x9cpin chambers.xe2x80x9d The pin chambers are in coaxial alignment with the first series of channels, and open upon said bore. The opposite extremities of the pin chambers, furthest from the bore, are closed. Each pin chamber confines a coil spring in abutment with said closed extremity, a driver pin and a tumbler pin. In some locks the several paired driver pins and tumbler pins are matched to have equal total lengths, and some locks have equal length driver pins with varying length tumbler pins. Both the driver pin and tumbler pin of each chamber are downwardly urged by said spring in a direction transverse to the axis of the plug, whereby the tumbler pins span the gap between the plug and housing.
The lengths of the tumbler pins, and their axial location determine the xe2x80x9ccodexe2x80x9d or key cut depths. When a properly configured key is inserted into the keyway of the plug, the tumbler pins are pushed up to a location flush with the outer surface of the plug, said location called a xe2x80x9cshear line.xe2x80x9d When all the tumbler pins are flush with the surface of the plug, the shear line is xe2x80x9copen,xe2x80x9d and rotation of the plug is permitted. The extent of pushed displacement of the tumbler pins to achieve an open shear line may be referred to as the xe2x80x9ctravel distancexe2x80x9d for a given tumbler pin. The pushing action is achieved by the key acting upon the lowermost extremity of the tumbler pin, which serves as a bearing surface. If a tumbler pin crosses the shear line, the plug will not rotate.
Wafer locks, like tumbler locks, have a cylindrical key receiving plug rotatably secured within a close fitting bore in a housing. The plug holds a series of flat apertured wafers adapted to undergo sliding movement in planes transverse to the axis of elongation of the plug. An outermost edge of each wafer is adapted to enter an aligned locking groove within the bore, and the wafers are spring urged to cause such entrance into the grooves, thereby preventing rotation of the bore in the locked state of the lock.
The aperture of each wafer has an upper edge bearing surface whose distance of separation from said axis varies amongst the several wafers. A key inserted into the plug sequentially penetrates the apertures of the wafers while bearing against said upper edges. Such action causes sliding movement of the wafers against the urging of said spring interactive with each wafer. The sequential sliding movement of the wafers causes the outermost extremities of the wafers to align themselves with the surface of the plug, thereby establishing a shear line which permits rotation of the plug. The axial location of each wafer, and the radial location of the upper edge of the aperture determine the key code for a particular lock.
When a key for a specific lock is lost, it often becomes necessary to analyze the lock to ascertain the requisite code for producing a replacement key. Probe devices for determining the key cuts of locks have earlier been disclosed, as for example in U.S. Pat. Nos. 4,535,546; 4,680,870; 5,224,365; 5,325,691; and 5,172,578. Such earlier devices are based upon mechanical principles of operation, and are often limited to use on certain models of locks, unless significant change is made in the probe device. Such earlier probe devices are also usually difficult to operate or require time-consuming manipulations, and are often of considerable cost.
It is accordingly an object of the present invention to provide a system for decoding tumbler and wafer locks.
It is another object of this invention to provide a system as in the foregoing object for ascertaining key cuts, and having versatility of use in many different models of locks.
It is a further object of the present invention to provide a system of the aforesaid nature for easily and rapidly ascertaining key cuts for locks.
It is a still further object of this invention to provide a decoding system of the aforesaid nature of durable and simple construction amenable to low cost manufacture.
These objects and other objects and advantages of the invention will be apparent from the following description.
The above and other beneficial objects and advantages are accomplished in accordance with the present invention by a system for decoding tumbler locks and wafer locks having a rotatably mounted cylindrical plug having an elongated key receiving slot interactive with a series of slideable members spring urged orthogonally toward said slot and having different travel distances relative to flush fit with the surface of said plug, said flush fit establishing a shear line which permits rotation of the plug, said system comprising:
a) a probe device having the general contour of a key expected to fit within said key-receiving slot and having:
1) a straight shank fabricated of electrically insulative material and elongated between forward and rearward extremities and bounded by opposed flat side surfaces and straight parallel upper and lower edge surfaces, and terminating in a tip portion having an oblique ramp surface extending forwardly from said upper edge surface and convergent toward said lower edge surface, said ramp surface configured to sequentially contact said slideable members,
2) a series of spaced apart electrical conductors embedded within said shank in parallel relationship to said edge surfaces and forwardly terminating in electrical contacts in said ramp surface, and
3) a head portion associated with the rearward extremity of said shank to facilitate manipulation of the probe device, and equipped with electrical contacts interactive with each electrical conductor,
b) electronic monitoring and display means interactive with said electrical conductors by way of said terminals and serving to indicate an individual conductor and its distance from the upper edge surface of said shank, said distance corresponding to the travel distance of a slideable member touching the corresponding electrical contact,
c) a source of low voltage direct current adapted to flow through said lock, shank and electronic monitoring and display means, and
d) correlation means for associating the indicated travel distance with a particular slideable member.
In employing the system of this invention, the probe is fully inserted into the key-receiving slot, then slowly withdrawn. As the probe is being withdrawn, the vertical travel distance for each slideable member is measured as the lowermost or bearing surface of the member slides down the ramp to its greatest depth, as sensed by the conductors. Said depth is read by said electronic monitoring and display means and correlated with the axial distance of insertion of said shank or the numerical sequence of a particular slideable member.
In a preferred embodiment, the probe includes an auxiliary shank which insertively engages the lower border surface of the key receiving slot, and provides an upper bearing surface for sliding support of the lower edge surface of said shank.